1. Field of Invention
The present invention relates to a switching regulator control circuit; particularly, it relates to a switching regulator control circuit with output short-circuit quick-response protection function.
2. Description of Related Art
For safety protection, a switching regulator control circuit needs to shut down output power from a switching regulator when an abnormal condition occurs which causes the current to exceed a current limit for a period of time.
FIG. 1 shows a schematic circuit diagram of a prior art AC-DC switching power converter circuit. As shown in FIG. 1, a switching regulator 10 converts an input voltage from an input terminal Vin to an output voltage by a transformer 11, and supplies the output voltage to an output terminal Vout. The transformer 11 includes a primary winding and a secondary winding. An optocoupler 12 is provided, for transmitting a feedback signal COMP to a switching regulator control circuit 20. The switching regulator control circuit 20 provides a switching signal GATE for controlling a power transistor switch 13. An input current IL through the power transistor switch 13 flows through a resistor Rcs, and the switching regulator control circuit 20 obtains the voltage across the resistor Rcs as a primary side input current sense signal CS. The switching regulator control circuit 20 generates an over current protection signal according to the input current sense signal CS and the feedback signal COMP. When the over current protection signal exceeds a current limit for a predetermined period of time, the switching regulator control circuit 20 outputs a short circuit protection signal for safety protection.
The conventional over current protection (OCP) mechanism is to compare a circuit current (input or output current) with a predetermined upper limit, and to count the time period in which the circuit current is over the upper limit. When the time period reaches a predetermined threshold, the circuit triggers an OCP protection measure. However, if the over current condition is caused by output short-circuit, a very large amount of current will be generated within a very short time, and this may cause damages to the circuit before the OCP protection measure is triggered. The OCP mechanism in the prior art switching regulator control circuit is designed for general over current conditions, but it can not respond in time to output short-circuit condition.
In view of the foregoing, the present invention provides a switching regulator control circuit with output short-circuit quick-response protection function. The present invention can distinguish the output short-circuit condition, which imposes immediate danger, from other mild over current conditions, to improve the safety protection for the switching regulator. Moreover, the present invention does not require complicated circuitry which consumes large area.